1. Field
Embodiments relate to an antenna device in which a radio communication device may receive a radio signal.
2. Description of the Related Art
Antenna devices for radio communication have been developed in a related art to be applied to portable terminals to send/receive radio signals.
An antenna device of the related art may be classified into an internal antenna and an external antenna according to whether the antenna device is accommodated in a terminal housing. Examples of the internal antenna may include a loop antenna, an inverted-L antenna, a planar inverted-F antenna (PIFA), etc. A monopole-type antenna or a rod-type antenna is mainly used as the external antenna.
Regarding an antenna of the related art, a physical length is determined by an electrical resonance length, which varies according to an operating frequency. Also, the physical length of the antenna may vary by a specific situation or a complicated structure. However, a range, in which the physical length of the antenna varies, is narrow. In particular, the monopole-type antenna, which is mainly used as the external antenna, has a simple shape. Thus, it is difficult to make the monopole-type antenna small.
A terrestrial digital multimedia broadcasting (DMB) has been used in the related art. A portable terminal market adds a broadcasting signal receiving function to a terminal in the related art. However, a frequency band used in a terrestrial DMB service is allocated in a range between about 180 MHz to about 186 MHz or between about 204 MHz to about 210 MHz. This frequency band is different from a frequency band of a mobile communication service used in the related art. Thus, it is difficult to provide the terrestrial DMB service through a related art portable terminal. In other words, an antenna device installed in the related art portable terminal is set to operate in a frequency band equal to or more than about 800 MHz. Thus, the antenna device of the related art is not proper for the terrestrial DMB service. In the antenna device proper for a frequency band used in the terrestrial DMB service, a length, protrudes out of a terminal, is as long as about 37 cm. This length corresponds to a quarter-wave, based on a frequency band of 200 MHz. In a related art, there have been attempts to reduce a protruding length of an antenna up to 20 cm by inserting a helical coil into the antenna. However, in view of a related art portable terminal having a major axis of about 10 cm, aesthetics and portability is greatly decreased in an antenna with a protruding length of 20 cm. Further, a complicated folding structure for accommodating the protruding length of 20 cm, in an apparatus of 10 cm, should be accomplished.